Methods and systems for adaptive base flow and leak compensation

ABSTRACT

This disclosure describes systems and methods for providing adaptive base flow scheduling during ventilation of a patient to optimize patient-machine synchrony and accuracy of estimated exhaled as well as inhaled tidal volumes. Further, this disclosure describes systems and methods for providing adaptive inspiratory trigger threshold scheduling during the adaptive base flow scheduling. Further still, this disclosure describes systems and methods for determining an estimated leak flow and adjusting the adaptive base flow scheduling and the adaptive inspiratory trigger threshold scheduling based on the estimated leak flow. Moreover, this disclosure describes systems and methods for determining a change in the estimated leak flow and adjusting the adaptive base flow scheduling and the adaptive inspiratory trigger threshold scheduling based on the change in the estimated leak flow.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 13/341,957 (now U.S. Pat. No. 9,498,589), entitled“METHODS AND SYSTEMS FOR ADAPTIVE BASE FLOW AND LEAK COMPENSATION,”filed on Dec. 31, 2011, the entire disclosure of which is herebyincorporated herein by reference.

INTRODUCTION

Medical ventilator systems have long been used to provide ventilatoryand supplemental oxygen support to patients. These ventilators typicallycomprise a source of pressurized oxygen which is fluidly connected tothe patient through a conduit or tubing. Further, ventilators oftenmeasure and calculate various ventilator and/or patient parametersduring the ventilation of a patient. For example, patient-ventilatorsynchrony and spirometry are major features with significant clinicalutility. Patient-ventilator synchrony ensures timely and adequateventilator response to patient's respiratory efforts. Spirometry dataprovides valuable information for patient evaluation and clinicaldecision making. Accordingly, synchrony (i.e., appropriate triggeringfrom exhalation into inhalation and cycling from inhalation intoexhalation) and accuracy of the spirometry data is an importantperformance characteristic of ventilators. Leak-compensated ventilationaims to ensure optimum synchrony and spirometry data in the presence ofsystem leak conditions.

Methods and Systems for Adaptive Base Flow and Leak Compensation

This disclosure describes systems and methods for providing adaptivebase flow scheduling during ventilation of a patient to optimizepatient-machine synchrony and accuracy of estimated exhaled as well asinhaled tidal volumes. Further, this disclosure describes systems andmethods for providing adaptive inspiratory trigger threshold schedulingduring the adaptive base flow scheduling. Further still, this disclosuredescribes systems and methods for determining an estimated leak flow andadjusting the adaptive base flow scheduling and the adaptive inspiratorytrigger threshold scheduling based on the estimated leak flow. Moreover,this disclosure describes systems and methods for determining a changein the estimated leak flow and adjusting the adaptive base flowscheduling and the adaptive inspiratory trigger threshold schedulingbased on the change in the estimated leak flow.

According to embodiments, a method is provided for ventilating a patientwith a ventilator. The method comprises delivering a base flow to apatient during exhalation, wherein the base flow includes an estimatedleak flow. Moreover, the method comprises determining an initial baseflow, determining an initial inspiratory trigger threshold, anddelivering the initial base flow during at least a first portion of theexhalation while setting an inspiratory trigger threshold to the initialinspiratory trigger threshold. The method further comprises changing thebase flow from the initial base flow toward a desired base flow duringat least a second portion of exhalation and decreasing an inspiratorytrigger threshold from the initial inspiratory trigger threshold towarda desired inspiratory trigger threshold while performing the step ofincreasing or decreasing the base flow. Moreover, the method comprisesdetermining a change in the estimated leak flow; and progressivelyadjusting the base flow in a set time period during the exhalation tocompensate for the determined change in the estimated leak flow whileadjusting the inspiratory trigger threshold in the set time period.

According to further embodiments, a ventilator system is providedcomprising a pressure generating system adapted to generate a flow ofbreathing gas, a ventilation tubing system including a patient interfacefor connecting the pressure generating system to a patient, and at leastone sensor operatively coupled to at least one of the pressuregenerating system and the ventilation tubing system. The ventilatorsystem further comprising a leak estimation module, wherein the leakestimation module determines a change in the estimated leak flow in theventilation tubing system by utilizing output from the at least onesensor. Furthermore, the ventilator system comprising a base flowtrajectory module, wherein the base flow trajectory module delivers abase flow including the estimated leak flow during exhalation to thepatient, wherein the base flow trajectory module changes the base flowdelivered to the patient from an initial base flow toward a desired baseflow during at least a portion of the exhalation, and wherein the baseflow trajectory module progressively adjusts the base flow during a settime period during the exhalation to compensate for the determinedchange in the estimated leak flow. The ventilator system also comprisingan inspiratory trigger threshold trajectory module, wherein theinspiratory trigger threshold trajectory module sets an inspiratorytrigger threshold during exhalation, wherein the inspiratory triggerthreshold trajectory module decreases the inspiratory trigger thresholdfrom an initial inspiratory trigger threshold towards a desiredinspiratory trigger threshold while the base flow trajectory modulechanges the base flow delivered to the patient. The ventilator systemfurther comprising a processor in communication with the pressuregenerating system, the at least one sensor, the leak estimation module,the inspiratory trigger threshold trajectory module, and the base flowtrajectory module.

According to further embodiments, a computer-readable medium havingcomputer-executable instructions for performing a method of ventilatinga patient with a ventilator is provided. The method comprisingdelivering a base flow to a patient during exhalation, where in the baseflow includes an estimated leak flow. The method further comprisingdetermining an initial base flow, determining an initial inspiratorytrigger threshold, and delivering the initial base flow during at leasta first portion of the exhalation while setting an inspiratory triggerthreshold to the initial inspiratory trigger threshold. The methodfurther comprising changing the base flow from the initial base flowtoward a desired base flow during at least a second portion ofexhalation and decreasing an inspiratory trigger threshold from theinitial inspiratory trigger threshold toward a desired inspiratorytrigger threshold while performing the step of increasing or decreasingthe base flow. Moreover, the method comprising determining a change inthe estimated leak flow and progressively adjusting the base flow in aset time period during the exhalation to compensate for the determinedchange in the estimated leak flow while adjusting the inspiratorytrigger threshold in the set time period.

According to further embodiments, a ventilator system is providedcomprising means for delivering a base flow to a patient duringexhalation, where in the base flow includes an estimated leak flow. Theventilator system further comprising means for determining an initialbase flow and means for determining an initial inspiratory triggerthreshold. The ventilator system also comprising means for changing thebase flow from an initial base flow toward a desired base flow during atleast a portion of exhalation and means for decreasing the inspiratorytrigger threshold from the initial inspiratory trigger threshold towarda first trigger threshold value while performing the step of increasingor decreasing the base flow. The ventilator system further comprisingmeans for determining a change in the estimated leak flow and means forprogressively adjusting the base flow in a set time period during theexhalation to compensate for the determined change in the estimated leakflow while adjusting the inspiratory trigger threshold for the set timeperiod.

These and various other features as well as advantages whichcharacterize the systems and methods described herein will be apparentfrom a reading of the following detailed description and a review of theassociated drawings. Additional features are set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the technology. Thebenefits and features of the technology will be realized and attained bythe structure particularly pointed out in the written description andclaims hereof as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawing figures, which form a part of this application,are illustrative of embodiments of systems and methods described belowand are not meant to limit the scope of the invention in any manner,which scope shall be based on the claims appended hereto.

FIG. 1 illustrates an embodiment of a ventilator.

FIG. 2 illustrates an embodiment of a method for ventilating a patienton a ventilator.

FIG. 3A illustrates an embodiment of a first portion of a method forventilating a patient on a ventilator.

FIG. 3B illustrates an embodiment of a second portion of the methodshown in FIG. 3A for ventilating a patient on a ventilator.

FIG. 4 illustrates an embodiment of a graph of delivered base flow and aset inspiratory trigger threshold over time during an exhalation.

DETAILED DESCRIPTION

Although the techniques introduced above and discussed in detail belowmay be implemented for a variety of medical devices, the presentdisclosure will discuss the implementation of these techniques in thecontext of a medical ventilator for use in providing ventilation supportto a human patient. A person of skill in the art will understand thatthe technology described in the context of a medical ventilator forhuman patients could be adapted for use with other systems such asventilators for non-human patients and general gas transport systems.

Medical ventilators are used to provide a breathing gas to a patient whomay otherwise be unable to breathe sufficiently. In modern medicalfacilities, pressurized air and oxygen sources are often available fromwall outlets. Accordingly, ventilators may provide pressure regulatingvalves (or regulators) connected to centralized sources of pressurizedair and pressurized oxygen. The regulating valves function to regulateflow so that respiratory gas having a desired concentration of oxygen issupplied to the patient at desired pressures and rates. Ventilatorscapable of operating independently of external sources of pressurizedair are also available.

Spirometry data provides valuable information for patient evaluation andclinical decision making. Accordingly, the accuracy of the spirometrydata is an important performance characteristic of ventilators.Spirometry volumes may be calculated by integrating the net flow, whichis a linear combination of flow rates measured by a number of flowsensors at both the inspiratory (delivery) side and at the exhalation(exhaust) side. These flow sensors possess different uncertainties andthe overall accuracy performance is a function of a combination of theproperties of individual devices. Exhaled tidal volume is measuredduring the expiratory phase of a ventilator breath while a base flow isdelivered through the patient circuit. To determine the volume of gasinhaled or exhaled by the patient, the net flow (total delivered flowminus total flow through exhalation module) is used for integration.That is, the delivered base flow is subtracted from the sum of the baseflow and patient flow exiting through the exhalation port. Deliveredflow during exhalation is base flow and consists of a desiredcombination of appropriate gases. The flow exiting the exhalation moduleduring the active phase of patient exhalation is the sum of base flowdelivered by the ventilator and exhaled flow from the patient lung. Theflow entering the patient's lung during inhalation is the algebraic sumof the total delivered flow minus the flow compressed in the tubing andany flow exiting through the exhalation module. According toembodiments, for both inhalation spirometry and exhalation spirometry,the flow (volume) lost through tubing leaks should be accounted foraccordingly. The spirometry parameter of exhaled tidal volume ismeasured during patient's active exhalation. Therefore, the smaller theventilator-delivered base flow is during active exhalation, the smallerthe uncertainty contributed by measuring the same quantity by differentsensors (once on the delivery side and a second time as a portion ofexhaust gas on the exhalation side). This is particularly advantageousunder neonatal conditions when tidal volumes and exhaled flow rates arerelatively smaller and may be some orders of magnitude smaller than thebase flow.

Accordingly, the systems and methods described herein provideventilation with an adaptive base flow initiation scheduling strategy tooptimize the accuracy of estimated exhaled tidal volume. However,changing base flow during exhalation may affect inspiratory triggeringand may lead to a false triggering of inspiration prior to a patientdesired inspiration. Accordingly, the systems and methods describedherein also provide ventilation with an adaptive trigger thresholdinitiation scheduling strategy to prevent undesired triggering ofinspiration. For example, if a change in leak size is detected justprior to or at the beginning of exhalation and a transition of base flowlevel is to be executed, then, during a first exhalation portion whenpatient-initiated triggering is unlikely, the inspiratory triggerthreshold is set relatively high. However, during a second exhalationperiod, when patient-initiated triggering is more likely, theinspiratory trigger threshold is reduced. Therefore, as exhalationprogresses or during a second portion exhalation, the inspiratorytrigger threshold is decreased making it easier for a patient toinitiate a desired inspiration. Similarly, if a change in leak size isdetected during ongoing exhalation and a base flow transition isexecuted, then, during a first transitory period the inspiratory triggerthreshold is adjusted appropriately to prevent false triggering duringthe base flow level change and subsequently adjusted towards the desiredlevel in a smooth fashion in coordination with the smooth transition ofthe base flow level to its final magnitude.

According to embodiments, the adaptive base flow initiation schedulingstrategy is further adjusted to account for estimated leak flow from theventilation tubing circuit. For example, a change in leak flow duringexhalation changes the amount of base flow the patient tubing receives,which can provide the system with too much or too little flow duringexhalation. When base flow is too high, this may cause patientdiscomfort; whereas if the base flow is too low, this may causeinaccurate triggering. Accordingly, the adaptive base flow initiationscheduling strategy is adjusted to account for changes in the estimatedleak flow detected during exhalation. Such changes in leak size, andconsequently in desired base flow, may occur at the beginning ofexhalation or at a certain point during the exhalation period. Asdiscussed above, adjustments in base flow during exhalation may affectinspiratory triggering and lead to a false triggering of inspirationprior to a patient desired inspiration. Accordingly, the systems andmethods described herein also provide ventilation with an adaptivetrigger threshold initiation scheduling strategy that is adjusted duringthe time period the base flow is adjusted (i.e., according to theadaptive base flow initiation scheduling strategy) to account fordetected changes in estimated leak flow to prevent undesired triggeringof inspiration.

FIG. 1 is a diagram illustrating an embodiment of an exemplaryventilator 100 connected to a human patient 150. Ventilator 100 includesa pneumatic system 102 (also referred to as a pressure generating system102) for circulating breathing gases to and from patient 150 via theventilation tubing system 130, which couples the patient 150 to thepneumatic system 102 via an invasive (e.g., endotracheal tube, as shown)or a non-invasive (e.g., nasal mask) patient interface 180.

Ventilation tubing system 130 (or patient circuit 130) may be a two-limb(shown) or a one-limb circuit for carrying gases to and from the patient150. In a two-limb embodiment, a fitting, typically referred to as a“wye-fitting” 170, may be provided to couple a patient interface 180 (asshown, an endotracheal tube) to an inspiratory limb 132 and anexpiratory limb 134 of the ventilation tubing system 130.

Pneumatic system 102 may be configured in a variety of ways. In thepresent example, pneumatic system 102 includes an expiratory module 108coupled with the expiratory limb 134 and an inspiratory module 104coupled with the inspiratory limb 132. Compressor 106 or other source(s)of pressurized gases (e.g., air, oxygen, and/or helium) is coupled withinspiratory module 104 and the expiratory module 108 to provide a gassource for ventilatory support via inspiratory limb 132.

The inspiratory module 104 is configured to deliver gases to the patient150 according to prescribed ventilatory settings. In some embodiments,inspiratory module 104 is configured to provide ventilation according tovarious breath types.

The expiratory module 108 is configured to release gases from thepatient's lungs according to prescribed ventilatory settings. Theexpiratory module 108 is associated with and/or controls an expiratoryvalve for releasing gases from the patient 150. Further, the expiratorymodule 108 may instruct the pressure generating system 102 and/or theinspiratory module 104 to deliver a base flow during exhalation.

The ventilator 100 may also include one or more sensors 107communicatively coupled to ventilator 100. The sensors 107 may belocated in the pneumatic system 102, ventilation tubing system 130,and/or on the patient 150. The embodiment of FIG. 1 illustrates a sensor107 in pneumatic system 102.

Sensors 107 may communicate with various components of ventilator 100,e.g., pneumatic system 102, other sensors 107, expiratory module 108,inspiratory module 104, processor 116, controller 110, trigger module115, inspiratory trigger trajectory module 117 (illustrated as “ITTModule”), base flow trajectory module 118 (illustrated as “Base FlowTraj. Module”), Leak Estimation Module 119 (illustrated as “Leak Est.Module), and any other suitable components and/or modules. In oneembodiment, sensors 107 generate output and send this output topneumatic system 102, other sensors 107, expiratory module 108,inspiratory module 104, processor 116, controller 110, trigger module115, inspiratory trigger trajectory module 117, base flow trajectorymodule 118, leak estimation module 119, and any other suitablecomponents and/or modules.

Sensors 107 may employ any suitable sensory or derivative technique formonitoring one or more patient parameters or ventilator parametersassociated with the ventilation of a patient 150. Sensors 107 may detectchanges in patient parameters indicative of patient inspiratory orexpiratory triggering, for example. Sensors 107 may be placed in anysuitable location, e.g., within the ventilatory circuitry or otherdevices communicatively coupled to the ventilator 100. Further, sensors107 may be placed in any suitable internal location, such as, within theventilatory circuitry or within components or modules of ventilator 100.For example, sensors 107 may be coupled to the inspiratory and/orexpiratory modules for detecting changes in, for example, circuitpressure and/or flow. In other examples, sensors 107 may be affixed tothe ventilatory tubing or may be embedded in the tubing itself.According to some embodiments, sensors 107 may be provided at or nearthe lungs (or diaphragm) for detecting a pressure in the lungs.Additionally or alternatively, sensors 107 may be affixed or embedded inor near wye-fitting 170 and/or patient interface 180. Indeed, anysensory device useful for monitoring changes in measurable parametersduring ventilatory treatment may be employed in accordance withembodiments described herein.

As should be appreciated, with reference to the Equation of Motion,ventilatory parameters are highly interrelated and, according toembodiments, may be either directly or indirectly monitored, That is,parameters may be directly monitored by one or more sensors 107, asdescribed above, or may be indirectly monitored or estimated byderivation according to the Equation of Motion or other knownrelationships.

The pneumatic system 102 may include a variety of other components,including mixing modules, valves, tubing, accumulators, filters, etc.Controller 110 is operatively coupled with pneumatic system 102, signalmeasurement and acquisition systems, and an operator interface 120 thatmay enable an operator to interact with the ventilator 100 (e.g., changeventilator settings, select operational modes, view monitoredparameters, etc.).

In one embodiment, the operator interface 120 of the ventilator 100includes a display 122 communicatively coupled to ventilator 100.Display 122 provides various input screens, for receiving clinicianinput, and various display screens, for presenting useful information tothe clinician. In one embodiment, the display 122 is configured toinclude a graphical user interface (GUI). The GUI may be an interactivedisplay, e.g., a touch-sensitive screen or otherwise, and may providevarious windows and elements for receiving input and interface commandoperations. Alternatively, other suitable means of communication withthe ventilator 100 may be provided, for instance by a wheel, keyboard,mouse, or other suitable interactive device. Thus, operator interface120 may accept commands and input through display 122.

Display 122 may also provide useful information in the form of variousventilatory data regarding the physical condition of a patient 150. Theuseful information may be derived by the ventilator 100, based on datacollected by a processor 116, and the useful information may bedisplayed to the clinician in the form of graphs, wave representations,pie graphs, text, or other suitable forms of graphic display. Forexample, patient data may be displayed on the GUI and/or display 122.Additionally or alternatively, patient data may be communicated to aremote monitoring system coupled via any suitable means to theventilator 100. In some embodiments, the display 122 may illustrate aminimum exhalation flow, a minimum exhalation time, a maximum exhalationtime, a desired base flow, a desired inspiratory trigger, an inspiratorytrigger, a base flow, an exhalation flow, an estimated leak flow, anexhalation pressure, and/or any other information known, received, orstored by the ventilator 100.

In some embodiments, controller 110 includes memory 112, one or moreprocessors 116, storage 114, and/or other components of the typecommonly found in command and control computing devices. Controller 110may further include an inspiratory trigger trajectory module 117, a baseflow trajectory module 118, a trigger module 115, and/or a leakestimation module 119 as illustrated in FIG. 1. In alternativeembodiments, the inspiratory trigger trajectory module 117, the baseflow trajectory module 118, trigger module 115, and/or the leakestimation module 119 are located in other components of the ventilator100, such as in the pressure generating system 102 (also known as thepneumatic system 102).

The memory 112 includes non-transitory, computer-readable storage mediathat stores software that is executed by the processor 116 and whichcontrols the operation of the ventilator 100. In an embodiment, thememory 112 includes one or more solid-state storage devices such asflash memory chips. In an alternative embodiment, the memory 112 may bemass storage connected to the processor 116 through a mass storagecontroller (not shown) and a communications bus (not shown). Althoughthe description of computer-readable media contained herein refers to asolid-state storage, it should be appreciated by those skilled in theart that computer-readable storage media can be any available media thatcan be accessed by the processor 116. That is, computer-readable storagemedia includes non-transitory, volatile and non-volatile, removable andnon-removable media implemented in any method or technology for storageof information such as computer-readable instructions, data structures,program modules or other data. For example, computer-readable storagemedia includes RAM, ROM, EPROM, EEPROM, flash memory or other solidstate memory technology, CD-ROM, DVD, or other optical storage, magneticcassettes, magnetic tape, magnetic disk storage or other magneticstorage devices, or any other medium which can be used to store thedesired information and which can be accessed by the computer.

The base flow trajectory module 118 determines the amount of base flowto deliver to the patient circuit tubing during exhalation. The baseflow trajectory module 118 adjusts the base flow based on an estimatedleak flow during exhalation. The base flow trajectory module 118receives the estimated leak flow from another component of theventilator 100, such as the controller 110, processor 116, and/or theleak estimation module 119.

The base flow trajectory module 118 delivers a constant base flow duringa first portion of exhalation and then varies the base flow deliveredduring at least a part of a second portion of exhalation. Accordingly,the base flow trajectory module 118 determines an initial base flow todeliver during a first portion of exhalation. In some embodiments, theinitial base flow is input or selected by the operator. In otherembodiments, the initial base flow is determined by the ventilator 100based on the configuration of the ventilator 100 and/or based onventilator and/or patient parameters and settings. The first portion ofexhalation includes at least the beginning or start of the exhalationperiod. In some embodiments, the first portion of exhalation is aminimum exhalation time. The “minimum exhalation time” as referred toherein is a predetermined amount of time in which it is unlikely that apatient would desire to begin inspiration or would attempt to trigger aninspiration. The base flow trajectory module 118 instructs theinspiratory module 104 to deliver the initial base flow at the beginningof inhalation. In further embodiments, the base flow trajectory module118 delivers the initial base flow at the beginning of the first portionof exhalation or for the entire duration of the first portion ofexhalation.

The base flow trajectory module 118 may also determine a desired baseflow. In some embodiments, the desired base flow is input or selected bythe operator. In other embodiments, the desired base flow is determinedby the ventilator 100 based on the configuration of the ventilator 100and/or based on ventilator and/or patient parameters.

The base flow trajectory module 118 instructs the inspiratory module 104to change the delivered base flow from the initial base flow towards afirst flow value, such as the desired base flow, during at least asecond portion of exhalation. The second portion of exhalation does notoverlap with the first portion of exhalation. Accordingly, the secondportion of exhalation does not include the beginning of exhalation, butmay begin immediately thereafter.

The second portion of exhalation starts or begins based on theoccurrence of a condition. The base flow trajectory module 118 maydetermine the occurrence of the condition based on output received fromsensors 107. Accordingly, in some embodiments, the base flow trajectorymodule 118 instructs the inspiratory module 104 to change the base flowfrom the initial base flow towards the desired base flow afterdetermining the occurrence of a condition. In some embodiments, thecondition includes determining that a minimum exhalation time hasexpired, determining that a monitored exhalation flow is below theminimum exhalation flow; determining that the monitored exhalation flowis below the minimum exhalation flow prior to expiration of a maximumexhalation time, and/or determining that the maximum exhalation time hasexpired. In other embodiments, the condition includes determining that aminimum exhalation time has expired and determining that either amonitored exhalation flow is below the minimum exhalation flow prior toexpiration of a maximum exhalation time or the maximum exhalation timehas expired. The maximum exhalation time is a predetermined amount oftime after which it becomes highly likely that a patient would attemptto trigger inspiration. The minimum exhalation flow is a predeterminedflow rate that when exhaled by the patient indicates that a patient isapproaching the end of active exhalation. In some embodiments, the baseflow trajectory module 118 instructs the inspiratory module 104 tochange the delivered base flow from the initial base flow towards afirst flow value at the start of a second portion of exhalation or,according to some embodiments, for the entire duration of the secondportion exhalation.

In embodiments, the base flow trajectory module 118 instructs theinspiratory module 104 to change the base flow according to anexponential trajectory. In some embodiments, the exponential trajectoryis based on a time constant that is indicative of the expected responsetime from the initial point to the final desired flow target. The timeconstant may be determined by the ventilator 100 based on the ventilatorconfiguration or based on ventilator and/or patient parameters. In otherembodiments, the time constant is input or selected by the operator.

In further embodiments, the base flow trajectory module 118 instructsthe inspiratory module 104 to change the base flow until the deliveredbase flow is essentially or substantially the first flow value, such asa desired base flow, Once the delivered base flow substantially reachesthe first flow value, the base flow trajectory module 118 instructs theinspiratory module 104 to deliver the first flow value. The first flowvalue is substantially reached or essentially reached when theventilator 100 can no longer change the amount of base flow providedwithout reaching or exceeding the first flow value based on thesensitivity and precision of the ventilator components.

According to embodiments, if a change in leak size (leak flow rate) isdetected during the exhalation phase (e.g., past the initial restrictedperiod), the base flow should be adjusted accordingly. In this case, thebase flow trajectory module 118 instructs the inspiratory module 104 tochange the base flow in a smooth fashion (e.g., exponential ascend ordescend) towards the desired level. In such cases, the duration of thetransition as well as the initial magnitude for adjusting the triggersensitivity is determined by the timeline of the transition of the baseflow and the status of the patient's exhalation activity (e.g., thehigher the patient's expiratory effort, the lower the probability of anew breath trigger).

Ventilators 100, depending on their mode of operation, may triggerautomatically and/or in response to a detected change in a ventilatorand/or patient parameter. The trigger module 115 receives and/ordetermines one or more inspiratory trigger thresholds. In someembodiments, the trigger module 115 receives an inspiratory triggerthreshold from the ITT Module 117. In other embodiments, the triggermodule 115 determines an inspiratory trigger threshold based onventilator and/or patient parameters and/or the ventilatorconfiguration. For example, the ventilator may be preconfigured todeliver an inspiration after a predetermined amount of exhalation timeto prevent a patient from becoming under-ventilated. In otherembodiments, the trigger module 115 receives an inspiratory triggerthreshold from operator input or selection.

During exhalation, the trigger module 115 monitors ventilator and/orpatient parameters and compares these parameters to one or moreinspiratory trigger thresholds to determine if the parameters meetand/or exceed the inspiratory trigger thresholds. Sensors 107 suitablefor this detection may include any suitable sensing device as known by aperson of skill in the art for a ventilator 100. If the trigger module115 determines that ventilator and/or patient parameters meet and/orexceed an inspiratory trigger threshold during exhalation, the triggermodule 115 instructs the inspiratory module 104 to deliver aninspiration, which effectively ends the exhalation phase controlled bythe expiratory module 108. If the trigger module 115 determines thatventilator and/or patient parameters do not meet and/or exceed aninspiratory trigger threshold during exhalation, the trigger module 115continues to monitor the ventilator and/or patient parameters andcompare them to a trigger threshold until the ventilator and/or patientparameters meet and/or exceed a trigger threshold.

In some embodiments, the trigger module 115 of the ventilator 100detects changes in a ventilator and/or patient parameter via themonitoring of a respiratory gas pressure, the monitoring of lung flow,direct or indirect measurement of nerve impulses, or any other suitablemethod for detecting changes in a ventilator parameter for comparison toan inspiratory trigger threshold. In embodiments where changes in aventilator parameter are detected by monitoring flow and/or pressure,the sensitivity of the ventilator 100 to changes in pressure and/orflow, may be adjusted. For example, the lower a pressure or flow changetrigger threshold setting, the more sensitive the ventilator 100 may beto a patient initiated trigger. However, each ventilator 100 will have aminimum measurable inspiratory flow and thereby have a change in flowthat the ventilator 100 cannot detect. Accordingly, a monitoredparameter below a minimum measurable value will not be detected by theventilator 100.

According to an embodiment, a pressure-triggering method may involve thetrigger module 115 of the ventilator 100 monitoring the circuitpressure, and detecting a slight drop in circuit pressure. The slightdrop in circuit pressure may indicate that the patient's respiratorymuscles are creating a slight negative pressure that in turn generates apressure gradient between the patient's lungs and the airway opening inan effort to inspire. The ventilator 100 may interpret the slight dropin circuit pressure as a patient trigger and may consequently initiateinspiration by delivering respiratory gases.

Alternatively, the trigger module 115 of the ventilator 100 may detect aflow-triggered event. Specifically, the trigger module 115 of theventilator 100 may monitor the circuit flow, as described above. If theventilator 100 detects a slight drop in the base flow through theexhalation module during exhalation, this may indicate that the patient150 is attempting to inspire. In this case, the ventilator 100 isdetecting a drop in base flow attributable to a slight redirection ofgases into the patient's lungs (in response to a slightly negativepressure gradient as discussed above). Accordingly, changes in base flowas instructed by the base flow trajectory module 118 may, if the triggerthreshold is set too low, trigger an unwanted inspiration.

The inspiratory trigger trajectory module 117 (illustrated as the “ITTModule”) determines a patient initiated inspiratory trigger threshold.The ITT module 117 sends the determined inspiratory trigger threshold toanother component of the ventilator, such as the controller 110,processor 116, and/or the trigger module 115. The trigger module 115, asdiscussed above, monitors the ventilator and/or patient parameters todetermine if the parameters meet and/or exceed the inspiratory triggerthreshold. The ITT module 117 continuously updates the inspiratorytrigger threshold. Accordingly, the ITT module 117 may send differentinspiratory trigger thresholds during different portions of exhalation.

The ITT module 117 determines and sets an initial inspiratory triggerthreshold while delivering the initial base flow. In some embodiments,the initial inspiratory trigger threshold is input or selected by theoperator. In other embodiments, the initial inspiratory triggerthreshold is determined by the ventilator 100 based on the configurationof the ventilator and/or based on ventilator parameters and/or patientparameters. The initial inspiratory trigger is set during at least thefirst portion of exhalation, which includes at least the beginning orstart of the exhalation period.

In some embodiments, in order to prevent undesirable early inspiratorytriggers, the inspiratory trigger may be set relatively high. Forexample, in some embodiments, the initial inspiratory trigger requires achange of flow of at least 6 liters per minute (LPM). In otherembodiments, the initial inspiratory trigger requires a change of flowof at least 8 LPM. In further embodiments, the initial inspiratorytrigger requires a change of flow of at least 10 LPM.

However, as the exhalation continues the likelihood that a patientdesires to initiate an inspiration increases. Accordingly, the ITTmodule 117 decreases an inspiratory trigger threshold during the secondportion of exhalation. The decrease in the inspiratory trigger thresholdrequires the patient to make less of an effort to trigger a desiredinspiration during the second portion of exhalation. Thus, the ITTmodule 117 decreases an inspiratory trigger threshold while the baseflow trajectory module 118 changes the base flow delivered to thepatient circuit tubing, as illustrated in FIG. 4.

In some embodiments, the ITT module 117 decreases the inspiratorytrigger at an exponential trajectory. In some embodiments, theexponential trajectory is based on a time constant. The time constantmay be determined by the ventilator 100 based on the ventilatorconfiguration or based on ventilator and/or patient parameters. In otherembodiments, the time constant is input or selected by the operator. Insome embodiments, the time constant utilized by the ITT module 117 isthe same time constant utilized by the base flow trajectory module 118to determine how to change the amount of base flow delivered to thepatient circuit tubing. In other embodiments, the ITT module 117decreases an inspiratory trigger threshold as a function of the amountthe base flow trajectory module 118 changes base flow or instructs theinspiratory module 104 to change base flow. In further embodiments, theITT module 117 decreases an inspiratory trigger threshold concurrentlywhile the base flow trajectory module 118 changes the base flowdelivered to the patient circuit tubing, as illustrated in FIG. 4(illustrating an increase in base flow concurrently with a decrease inthe inspiratory trigger threshold).

In some embodiments, the ITT module 117 also determines a firstinspiratory trigger threshold value, such as a desired inspiratorytrigger threshold. In some embodiments, the first inspiratory triggerthreshold value is input or selected by the operator. In otherembodiments, the first inspiratory trigger threshold value is determinedby the ventilator 100 based on the configuration of the ventilator 100and/or based on ventilator parameters and/or patient parameters. Inembodiments with a first inspiratory trigger threshold value, the ITTmodule 117 decreases the inspiratory trigger threshold from the initialinspiratory trigger threshold towards the first inspiratory triggerthreshold value, such as a desired inspiratory trigger threshold.

Accordingly, in some embodiments, the ITT module 117 decreases theinspiratory trigger threshold until the inspiratory trigger essentiallyor substantially reaches the first inspiratory trigger threshold value.Once the inspiratory trigger threshold substantially reaches the firstinspiratory trigger threshold value, the ITT module 117 sets theinspiratory trigger threshold value to the first inspiratory triggerthreshold value. The first inspiratory trigger threshold value issubstantially reached or essentially reached when the ventilator 100 canno longer decrease the inspiratory trigger threshold without reaching orpassing the first inspiratory trigger threshold value based on thesensitivity and precision of the ventilator components.

According to some embodiments, the base flow trajectory module 118allows the ventilator 100 to provide a lower base flow during a firstportion of exhalation and a higher base flow during a second portion ofexhalation or vice versa. When the ventilator delivers a lower base flowduring active exhalation (i.e., the first portion of exhalation), thereis less uncertainty caused by measuring base flow at different sensors107 (once on the delivery side and a second time as a portion of exhaustgas on the exhalation side). This is particularly advantageous underneonatal conditions when tidal volumes and exhaled flow rates arerelatively smaller and may be some orders of magnitude smaller than thebase flow. Accordingly, the base flow trajectory module 118 allows theprocessor 116 or controller 110 to more accurately calculate exhaledtidal volume and/or spirometry than ventilators that utilize a constantbase flow or a higher amount of base-flow during active exhalation.

The leak estimation module 119 estimates the amount of flow leaking fromthe ventilation tubing system 130. The leak estimation module 119 sendsthe estimated leak flow to other components of the ventilator 100, suchas the controller 110, processor 116, base flow trajectory module 118,pneumatic system 102, and/or display 122.

According to embodiments, the initial base flow includes the estimatedleak flow determined by leak estimation module 119. In some embodiments,the initial base flow is zero if there is no estimated leak flow and nodesired initial base flow. In alternative embodiments, the initial baseflow is at least equivalent to or greater than the estimated leak flow.The leak estimation module 119 estimates the amount of flow leaking fromthe ventilation tubing system 130 by utilizing any conventionally knownmethod for estimating leak flow from the ventilation tubing system 130.Additionally, with reference to embodiments described above, the firstflow value includes the estimated leak flow as determined by the leakestimation module 119 to compensate for the amount of flow lost from theventilation tubing system 130 during ventilation. Moreover, according toembodiments, the base flow trajectory module 118 utilizes the estimatedleak flow, as determined by the leak estimation module 119, to determinethe initial base flow and/or the first flow value.

Further, the leak estimation module 119 determines if there has been achange in the estimated leak flow during exhalation. In someembodiments, after a change in the estimated leak flow has beendetected, the leak estimation module 119 updates the estimated leak flowbased on the detected change. In embodiments, the leak estimation module119 determines if there has been a change in the estimated leak flowduring exhalation by monitoring one or more patient and/or ventilatorparameters or settings. In further embodiments, the leak estimationmodule 119 determines if there has been a change in the estimated leakflow during exhalation by monitoring output from one or more sensors107. The leak estimation module 119 determines a change in the amount offlow leaking from the ventilation tubing system 130 during exhalation byutilizing any conventionally known method for estimating leak flowand/or for detecting a change in the leak flow from the ventilationtubing system 130. The leak estimation module 119 sends the determinedchange in the estimated leak flow (or an updated estimated leak flowvalue) to other components of the ventilator 100, such as the controller110, processor 116, base flow trajectory module 118, ITT module 117,pneumatic system 102, and/or display 122.

According to embodiments, a change in leak flow during exhalation canimpact the base flow during exhalation, resulting in too much or toolittle base flow during exhalation and causing patient discomfort and/orinaccurate triggering. Accordingly, the determined change in estimatedleak flow is utilized by the base flow trajectory module 118 to adjustthe base flow during exhalation. For example, if an increase inestimated leak flow is detected during exhalation, base flow may beincreased. Alternatively, if a decrease in the estimated leak flow isdetected during exhalation, base flow may be decreased.

According to further embodiments, when the base flow trajectory module118 receives a determined change in the estimated leak flow, the baseflow trajectory module 118 progressively adjusts the base flow deliveredduring exhalation during a set time period to compensate for thedetermined change. The base flow trajectory module 118 may increase ordecrease the delivered base flow during exhalation depending upon thedetermined change in the estimated leak flow. As used herein“progressively adjust” refers to changing the base flow delivered in aplurality of increments during a set time period to compensate for thedetected change in estimated leak flow. For example, the base flowtrajectory module 118 may change the amount of base flow delivered overthe set time period in phases, in a step-wise pattern, and/or utilizingan exponential trajectory.

In some embodiments, the base flow is progressively adjusted utilizingan exponential trajectory based on a time constant. The time constantmay be the same time constant utilized by the ventilator during thesecond phase of exhalation to change the delivered base flow and/or todecrease the inspiratory trigger threshold. In some embodiments, theventilator determines the time constant. In other embodiments, the timeconstant is selected or input by an operator.

In alternative embodiments, the base flow is progressively adjusted as afunction of the determined change in the estimated leak flow. In someembodiments, the base flow is progressively adjusted based on percentagemultiplied by the determined change in the estimated leak flow, such asa percentage of 5%, 10%, 15%, 20%, 25%, etc. For example, if theestimated leak flow increases by 5 liters per min (LPM), the base flowtrajectory module 118 may progressively adjust the base flow deliveredduring exhalation during the set time period by 10% increments, e.g.,progressively increase the delivered base flow by increments of 0.50 LPMover the set time period until the base flow is increased by the 5 LPMincrease in estimated leak flow.

In some embodiments, the set time period is determined by the ventilator100. In some embodiments, the set time period is based on theconfiguration of the ventilator. In other embodiments, the set timeperiod is determined by the ventilator based on ventilator and/orpatient parameters or settings. In some embodiments, the set time perioddetermined by the ventilator is a function of the determined change inthe estimated leak flow. In alternative embodiments, the set time periodis selected or input by the operator. Is some embodiments, the set timeperiod is 200 milliseconds (ms) or less. In other embodiments, the settime period is 150 ms or less. In other embodiments, the set time periodis 125 ms or less.

When the ITT module 117 receives a determined change in the estimatedleak flow, the ITT module 117 adjusts the inspiratory trigger thresholdfor the set time period. For example, if the estimated leak flowincreases (resulting in a decreased base flow through the exhalationmodule), the inspiratory trigger threshold may also be increased,thereby decreasing trigger sensitivity and making it less probable for afalse determination of the patient inspiratory trigger. Alternatively,if the estimated leak flow decreases (resulting in an increase in baseflow through the exhalation module), the inspiratory trigger thresholdmay also be decreased for a transition period, thereby increasing theprobability of detecting the patient's effort to trigger inspiration.

In some embodiments, the inspiratory trigger threshold is increasedbased on a function of a detected increase in estimated leak flow. Inthis case, according to embodiments, the inspiratory trigger isincreased one time by a set amount for the duration of the set timeperiod. In alternative embodiments, the ITT module 117 progressivelyincreases the inspiratory trigger threshold for the set time period. Asused herein “progressively increases” refers to increasing theinspiratory trigger threshold in a plurality of increments during theset time period. For example, the ITT module 117 may increase theinspiratory trigger threshold during the set time period in phases, in astep-wise pattern, and/or by utilizing an exponential trajectory.

In further embodiments, the inspiratory trigger threshold isprogressively increased utilizing an exponential trajectory based on atime constant. The time constant may be the same time constant utilizedby the ventilator during the second phase of exhalation to increase thedelivered base flow and/or to decrease the inspiratory triggerthreshold. In some embodiments, the ventilator determines the timeconstant. In other embodiments, the time constant is selected or inputby an operator.

In some embodiments, the inspiratory trigger threshold is increasedbased on a percentage multiplied by the determined increase in theestimated leak flow, such as a percentage of 5%, 10%, 15%, 20%, 25%,etc. For example, if the estimated leak flow increases by 5 liters perminute (LPM) (decreasing base flow), the ITT module 117 may increase theinspiratory trigger threshold by 10% increments over a set time periodduring exhalation, e.g., 0.5 LPM each cycle, until the inspiratorytrigger threshold is increased by 5 LPM. According to embodiments, theITT module 117 may increase the inspiratory trigger threshold accordingto any suitable percentage, algorithm, protocol, etc.

According to alternative embodiments, the inspiratory trigger thresholdis decreased as a function of a detected decrease in estimated leakflow. In this case, the inspiratory trigger may be decreased one time bya set amount for the duration of the set time period. In alternativeembodiments, the ITT module 117 progressively decreases the inspiratorytrigger threshold for the set time period. As used herein “progressivelydecreases” refers to decreasing the inspiratory trigger threshold in aplurality of increments during the set time period. For example, the ITTmodule 117 may decrease the inspiratory trigger threshold during the settime period in phases, in a step-wise pattern, and/or by utilizing anexponential trajectory.

In further embodiments, the inspiratory trigger threshold isprogressively decreased utilizing an exponential trajectory based on atime constant. The time constant may be the same time constant utilizedby the ventilator during the second phase of exhalation to change thedelivered base flow and/or to decrease the inspiratory triggerthreshold. In some embodiments, the ventilator determines the timeconstant. In other embodiments, the time constant is selected or inputby an operator.

In some embodiments, the inspiratory trigger threshold is decreasedbased on a percentage multiplied by the determined decrease in theestimated leak flow, such as a percentage of 5%, 10%, 15%, 20%, 25%,etc. For example, if the estimated leak flow decreases by 5 liters perminute (LPM) (decreasing base flow), the ITT module 117 may decrease theinspiratory trigger threshold by 10% increments over a set time periodduring exhalation, e.g., 0.5 LPM each cycle, until the inspiratorytrigger threshold is decreased by 5 LPM. According to embodiments, theITT module 117 may decrease the inspiratory trigger threshold accordingto any suitable percentage, algorithm, protocol, etc.

According to alternative embodiments, during a second portion ofexhalation, the ITT Module 117 decreases the inspiratory triggerthreshold when the base flow is changed. During the second portion ofexhalation, it is more likely that the patient will trigger a desiredinspiration. As such, decreasing the inspiratory trigger thresholdincreases trigger sensitivity and makes it easier for the patient totrigger inspiration. According to additional embodiments, ITT Module 117adaptively adjusts the inspiratory trigger threshold during the secondperiod of exhalation based on detecting a change in estimated leak flow.That is, while the inspiratory trigger threshold may follow a generallydeclining exponential trajectory during the second portion ofexhalation, this declining exponential may be adjusted based ondetecting a change in the estimated leak flow (i.e., increasing theinspiratory trigger threshold upon detecting an increase in estimatedleak flow and decreasing the inspiratory trigger threshold upondetecting a decrease in estimated leak flow during the second portion ofexhalation).

FIG. 2 illustrates an embodiment of a method 200 for ventilating apatient with a ventilator. Method 200 begins at the start of exhalation.During exhalation the ventilator delivers a base flow to a patient. Thebase flow includes an estimated leak flow. According to embodiments,during a first portion of exhalation the ventilator delivers an initialbase flow to the patient circuit tubing. According to furtherembodiments, during a second portion of exhalation, the ventilatordelivers an adaptive base flow that changes exponentially from theinitial base flow toward a desired base flow. Additionally, duringexhalation the ventilator determines and sets an inspiratory triggerthreshold. For example, during exhalation the ventilator determines aninitial inspiratory trigger threshold and a desired inspiratory triggerthreshold. According to embodiments, during a first portion ofexhalation the ventilator sets an initial inspiratory trigger threshold.According to further embodiments, during a second portion of exhalationthe ventilator configures the inspiratory trigger threshold to decreaseexponentially from the initial inspiratory trigger threshold toward adesired inspiratory trigger threshold.

As illustrated, method 200 includes a first portion delivery operation202. According to embodiments, the first portion of exhalation includesat least the beginning or start of exhalation and does not overlap witha second portion of exhalation. In some embodiments, the first portionof exhalation includes a minimum exhalation time.

According to embodiments, the ventilator delivers an initial base flowto the patient at the start of or for the entire duration of a firstportion of exhalation during first portion delivery operation 202. Theinitial base flow includes an estimated leak flow. According toembodiments, the initial base flow may be predetermined by theventilator based on the configuration of the ventilator or determined bythe ventilator based on ventilator and/or patient parameters orsettings. In an alternative embodiment, the initial base flow may beinput or selected by an operator. According to further embodiments, theinitial base flow is automatically adjusted to account for an estimatedleak flow. According to embodiments, an amount of flow is added to theestimated leak flow in order to determine the initial base flow.According to embodiments, the amount of flow added may be predeterminedby the ventilator based on the configuration of the ventilator or may bedetermined by the ventilator based on ventilator and/or patientparameters or settings. In an alternative embodiment, the amount of flowadded to the estimated leak flow to determine the initial base flow isinput or selected by an operator.

According to additional embodiments, the ventilator during the firstportion delivery operation 202 determines an initial inspiratory triggerthreshold for the first portion of exhalation. According to embodiments,the initial inspiratory trigger threshold may be predetermined by theventilator based on the configuration of the ventilator or determined bythe ventilator based on ventilator and/or patient parameters orsettings. In an alternative embodiment, the initial inspiratory triggerthreshold may be input or selected by an operator.

In some embodiments, the initial base flow is a base flow of zero orclose to zero when the estimated leak flow is zero or close to zero. Inalternative embodiments, the initial base flow is at least equivalent toor greater than the estimated leak flow. In some embodiments, theinitial inspiratory trigger threshold is set relatively high. Duringearly exhalation it is unlikely that a patient actually desires totrigger an inspiration. Accordingly, to prevent monitored parametersfrom resulting in a false trigger of an undesired inspiration, a highinitial inspiratory trigger threshold may be utilized. For example, theinitial inspiratory trigger threshold may require a change of flow of atleast 6 to 10 LPM.

As illustrated, method 200 includes a change in estimated leak flowdecision operation 203 (illustrated as “Change in Est. Leak Flow?”). Theventilator during the change in estimated leak flow decision operation203 determines if there has been a change in the estimated leak flow.The ventilator monitors patient and/or ventilator parameters todetermine if there has been a change in the estimated leak flow duringexhalation. The estimated leak flow may be estimated by utilizing anyknown suitable methods or systems.

In some embodiments, method 200 detects changes in a ventilator and/orpatient parameter via monitoring of a respiratory gas pressure, themonitoring of lung flow, direct or indirect measurement of nerveimpulses, or any other suitable method for detecting changes in aventilator and/or patient parameters. Method 200 may utilize sensors tomonitor the ventilator and/or patient parameters. Sensors may includeany suitable sensing device as known by a person of skill in the art fora ventilator. In some embodiments, the ventilator monitors theventilator and/or patient parameters every computational cycle (e.g., 2milliseconds, 5 milliseconds, 10 milliseconds, etc.) during the deliveryof exhalation to determine if estimated leak flow has changed duringexhalation.

If the ventilator during change in estimated leak flow decisionoperation 203 determines that there has been a change in the estimatedleak flow, the ventilator selects to perform adjust operation 205. Ifthe ventilator during change in estimated leak flow decision operation203 determines that there has not been a change in the estimated leakflow, the ventilator selects to perform transition condition decisionoperation 204.

Method 200 also includes an adjust operation 205. The ventilator duringadjust operation 205 progressively adjusts the initial base flow duringa set time period during exhalation to compensate for the determinedchange in the estimated leak flow while also adjusting the inspiratorytrigger threshold for the set time period. For example, if theventilator determines estimated leak flow has increased (insufficientinitial base flow), the ventilator may increase the initial base flow tocompensate for the increase in estimated leak flow. Alternatively, ifthe ventilator determines estimated leak flow has decreased (excessiveinitial base flow), the ventilator may decrease the initial base flow tocompensate for the decrease in estimated leak flow. In some embodiments,after a change in the estimated leak has been detected, ventilatorduring the adjust operation 205 further estimates the updated estimatedleak flow based on the detected change during exhalation.

According to embodiments, the ventilator during adjust operation 205 mayincrease or decrease the initial base flow during exhalation dependingon the determined change in the estimated leak flow. As used herein“progressively adjusted” refers to incrementally changing the initialbase flow delivered during a set time period over a plurality of controlcycles (e.g., 2 ms control cycles, 5 ms control cycles, etc.) tocompensate for the detected change in estimated leak flow. For example,the ventilator during adjust operation 205 may change the amount ofinitial base flow delivered during the set time period in phases, in astep-wise pattern, and/or utilizing an exponential trajectory. The settime period for adjusting the initial base flow may be determined by theventilator, e.g., based on pre-established ventilator settings or basedon ventilator calculations. In alternative embodiments, the set timeperiod is selected or input by the operator. In some embodiments, asdescribed above, the initial base flow is progressively adjusted(increased or decreased) utilizing an exponential trajectory based on atime constant. In other embodiments, the initial base flow is adjusted(increased or decreased) based on a percentage multiplied by thedetermined change in the estimated leak flow, such as a percentage of5%, 10%, 15%, 20%, 25%, etc. According to embodiments, the initial baseflow may be increased according to any suitable percentage, algorithm,protocol, etc.

In additional embodiments, during adjust operation 205 the initialinspiratory trigger threshold is adjusted (increased or decreased) as afunction of the detected change (increase or decrease) in estimated leakflow. For example, if the ventilator determines estimated leak flow hasincreased (decreasing the initial base flow), the ventilator mayincrease the initial inspiratory trigger threshold to compensate for theincrease in estimated leak flow. In this case, the trigger sensitivityis decreased making it more difficult for the patient to triggerinspiration. Alternatively, if the ventilator determines estimated leakflow has decreased (increasing the initial base flow), the ventilatormay decrease the initial inspiratory trigger threshold to compensate forthe decrease in estimated leak flow. In this case, the triggersensitivity is increased making it easier for the patient to triggerinspiration.

According to further embodiments, the ventilator during adjust operation205 may increase or decrease the initial inspiratory trigger thresholdduring exhalation depending on the determined change in the estimatedleak flow. As used herein “progressively adjusted” refers toincrementally changing the initial inspiratory trigger thresholddelivered during a set time period over a plurality of control cycles(e.g., 2 ms control cycles, 5 ms control cycles, etc.) to compensate forthe detected change in estimated leak flow. For example, the ventilatorduring adjust operation 205 may change the initial inspiratory triggerthreshold during the set time period in phases, in a step-wise pattern,and/or utilizing an exponential trajectory. The set time period foradjusting the initial base flow may be determined by the ventilator orselected or input by the operator. In some embodiments, as describedabove, the initial inspiratory trigger threshold is progressivelyadjusted (increased or decreased) utilizing an exponential trajectorybased on a time constant. In other embodiments, the initial inspiratorytrigger threshold is adjusted (increased or decreased) based on apercentage multiplied by the determined change in the estimated leakflow, such as a percentage of 5%, 10%, 15%, 20%, 25%, etc. According toembodiments, the initial inspiratory trigger threshold may be increasedaccording to any suitable percentage, algorithm, protocol, etc.

Further, method 200 includes a transition condition decision operation204 (illustrated as “transition condition?”). During the transitioncondition decision operation 204, the ventilator determines if acondition has been met. The condition may include any suitablecondition, including determining that a minimum exhalation time hasexpired, determining that an exhalation flow is below the minimumexhalation flow, determining that the exhalation flow is below theminimum exhalation flow prior to expiration of a maximum exhalationtime, and/or determining that the maximum exhalation time has expired.The first portion of exhalation ends when the condition has been met.The second portion of exhalation begins when the condition has been met.

According to embodiments, if the ventilator during transition conditiondecision operation 204 determines that a condition has been met, theventilator selects to perform second portion delivery operation 206. Ifthe ventilator during transition condition decision operation 204determines that a condition has not been met, the ventilator selects toperform inspiratory trigger decision operation 209.

According to embodiments, during the second portion delivery operation206, the ventilator changes (i.e., increases or decreases) the base flowdelivered to the patient tubing is from the initial base flow toward adesired base flow during the second portion of exhalation. According toembodiments, the desired base flow is received via input or selection byan operator, e.g., via a graphical user interface, keyboard, mouse,and/or any other suitable input device for receiving and interpretingoperator commands, instructions, and/or selections. In an alternativeembodiment, the desired base flow is determined by the ventilator.

In some embodiments, the ventilator changes base flow from the initialbase flow toward the desired base flow at the start of or during theentire duration of the second portion of exhalation. According toalternative embodiments, the ventilator incrementally changes the baseflow from the initial base flow toward the desired base flow over aperiod of time. For example, the ventilator may incrementally change thebase flow from the initial base flow toward the desired base flow inphases, in a step-wise pattern, and/or by utilizing an exponentialtrajectory. That is, the ventilator may incrementally change the baseflow from the initial base flow toward the desired base flow to a firstflow value in a first control cycle and to a second flow value in asecond control cycle, etc.

In some embodiments, the ventilator during second portion deliveryoperation 206 changes the base flow from the initial base flow towardthe desired base flow until the desired base flow is reached orsubstantially reached. If the delivered base flow reaches orsubstantially reaches the desired base flow, the ventilator duringsecond portion delivery operation 206 delivers the desired base flowuntil inspiration is triggered by the patient. In some embodiments, theventilator during second portion delivery operation 206 changes the baseflow according to an exponential trajectory. In further embodiments, theventilator during second portion delivery operation 206 changes the baseflow according to an exponential trajectory based on a time constant.The time constant may be determined by the ventilator or input orselected by an operator.

Further, during the second portion delivery operation 206, theventilator decreases an inspiratory trigger threshold from the initialinspiratory trigger threshold toward a desired inspiratory triggerthreshold during at least a portion of the second portion of exhalation.Accordingly, in some embodiments, the ventilator concurrently orsimultaneously changes the delivered base flow as the ventilator lowersthe inspiratory trigger threshold during the second portion deliveryoperation 206.

In some embodiments, the ventilator during second portion deliveryoperation 206 decreases the inspiratory trigger threshold from theinitial inspiratory trigger threshold towards the desired inspiratorytrigger threshold until the desired inspiratory trigger threshold isreached or substantially reached. If the inspiratory trigger thresholdreaches or substantially reaches the desired inspiratory triggerthreshold, the ventilator during second portion delivery operation 206maintains the inspiratory trigger threshold at the desired inspiratorytrigger threshold until the patient triggers inspiration.

According to embodiments, the ventilator during second portion deliveryoperation 206 decreases the inspiratory trigger threshold at the startof or during the entire duration of the second portion of exhalation.According to alternative embodiments, the ventilator incrementallydecreases the inspiratory trigger threshold from the initial inspiratorytrigger threshold towards the desired inspiratory trigger threshold overa period of time. For example, the ventilator may incrementally decreasethe inspiratory trigger threshold from the initial inspiratory triggerthreshold towards the desired inspiratory trigger threshold in phases,in a step-wise pattern, and/or by utilizing an exponential trajectory.That is, the ventilator may incrementally decrease the inspiratorytrigger threshold from the initial inspiratory trigger threshold towardsthe desired inspiratory trigger threshold to a first flow value in afirst control cycle and to a second flow value in a second controlcycle, etc.

In some embodiments, the ventilator during second portion deliveryoperation 206 decreases the inspiratory trigger threshold according toan exponential trajectory. In further embodiments, the ventilator duringsecond portion delivery operation 206 decreases the inspiratory triggerthreshold at an exponential trajectory based on a time constant. In someembodiments, the time constant is determined by the ventilator or inputor selected by an operator. In further embodiments, the time constantmay be the same time constant utilized by the ventilator to determinethe amount to change the delivered base flow. In additional embodiments,the ventilator during second portion delivery operation 206 decreasesthe inspiratory trigger threshold as a function of the amount theventilator changes the delivered base flow.

In some embodiments, the ventilator may decrease the inspiratory triggerthreshold from the initial inspiratory trigger threshold towards thedesired inspiratory trigger threshold until the desired inspiratorytrigger threshold is substantially reached. If the set inspiratorytrigger threshold reaches or substantially reaches the desiredinspiratory trigger threshold, the ventilator during second portiondelivery operation 206 maintains the inspiratory trigger threshold atthe desired inspiratory trigger threshold until the patient triggersinspiration.

That is, method 200 decreases the inspiratory trigger threshold whilethe base flow is being changed. According to embodiments, the longer theexhalation period, the more likely the patient will attempt to initiatean inspiratory trigger. As such, decreasing the inspiratory triggerthreshold during the second portion of exhalation allows a patient toexert less effort to trigger a desired inspiration when it becomes morelikely that a patient will attempt to trigger an inspiration.

As illustrated, method 200 includes a change in estimated leak flowdecision operation 207 (illustrated as “Change in Est, Leak Flow?”).Change in estimated leak flow decision operation 207 is substantiallythat same as change in estimated leak flow decision operation 203,described above. That is, at change in estimated leak flow decisionoperation 207 the ventilator determines if there has been a change inthe estimated leak flow via any suitable means.

If the ventilator during change in estimated leak flow decisionoperation 207 determines that there has been a change in the estimatedleak flow, the ventilator selects to perform adjust operation 208. Ifthe ventilator during change in estimated leak flow decision operation207 determines that there has not been a change in the estimated leakflow, the ventilator selects to perform detect inspiratory triggerdecision operation 210.

At adjust operation 208, the ventilator progressively adjusts the baseflow during a set time period during the second period of exhalation tocompensate for the determined change in the estimated leak flow. Forexample, if the ventilator determines estimated leak flow has increased(insufficient base flow), the ventilator may increase the base flow tocompensate for the increase in estimated leak flow. Alternatively, ifthe ventilator determines estimated leak flow has decreased (excessivebase flow), the ventilator may decrease the base flow to compensate forthe decrease in estimated leak flow. According to embodiments, duringthe second portion of exhalation, base flow is adjusted from an initialbase flow to a desired base flow while also being adjusted based ondetecting a change in estimated leak flow.

Additionally, during adjust operation 208 the ventilator progressivelyadjusts the inspiratory trigger threshold during the set time period tocompensate for the determined change in the estimated leak flow. Forexample, if the ventilator determines estimated leak flow has increased(insufficient base flow), the ventilator may increase the inspiratorytrigger threshold to compensate for the increase in estimated leak flow.Alternatively, if the ventilator determines estimated leak flow hasdecreased (excessive base flow), the ventilator may decrease theinspiratory trigger threshold to compensate for the decrease inestimated leak flow. According to embodiments, during the second portionof exhalation, inspiratory trigger threshold is adjusted from an initialinspiratory trigger threshold to a desired inspiratory trigger thresholdwhile also being adjusted based on detecting a change in estimated leakflow.

As illustrated, method 200 includes an inspiratory trigger decisionoperation 209 (illustrated as “Detect Insp. Trigger?”). During theinspiratory trigger decision operation 209, the ventilator determines ifan inspiratory trigger has been detected. Inspiratory trigger decisionoperation 209 is performed during the first portion of exhalation.

The ventilator, during inspiratory trigger decision operation 209,monitors patient and/or ventilator parameters or settings to determineif an inspiratory trigger threshold has been met and/or exceeded duringthe first portion of exhalation. The inspiratory trigger thresholdincludes any suitable condition or threshold for determining thatinspiration should be provided to the patient. During the first portionof exhalation, the inspiratory trigger threshold includes the initialinspiratory trigger threshold as determined by first portion deliveryoperation 202.

In some embodiments, method 200 detects changes in a ventilator and/orpatient parameter via the monitoring of a respiratory gas pressure, themonitoring of lung flow, direct or indirect measurement of nerveimpulses, or any other suitable method for detecting changes in aventilator parameter for comparison to inspiratory trigger thresholds.Method 200 may utilize sensors to monitor the ventilator and/or patientparameters. Sensors may include any suitable sensing device as known bya person of skill in the art for a ventilator. In some embodiments, theinspiratory trigger threshold may be a change in exhalation pressure ora change in exhalation flow. In some embodiments, the sensors arelocated in the pneumatic system, the breathing circuit, and/or at thepatient. In some embodiments, the ventilator monitors the exhalationflow and/or exhalation pressure every computational cycle (e.g., 2milliseconds, 5 milliseconds, 10 milliseconds, etc.) during the deliveryof exhalation to determine if the inspiratory trigger threshold has beenmet and/or exceeded.

If the ventilator during inspiratory trigger decision operation 209determines that the ventilator and/or patient parameters do not meet orexceed an inspiratory trigger threshold, the ventilator selects toperform first portion delivery operation 202. If the ventilator duringinspiratory trigger decision operation 209 determines that theventilator and/or patient parameters do meet or exceed an inspiratorytrigger threshold, the ventilator selects to perform inhale operation211. The performance of the inhale operation 211 ends the exhalationphase.

Method 200 includes an inspiratory trigger decision operation 210(illustrated as “Detect Insp. Trigger?”). During the inspiratory triggerdecision operation 210, similar to inspiratory trigger decisionoperation 208, the ventilator determines if an inspiratory trigger hasbeen detected. Inspiratory trigger decision operation 210 is performedduring the second portion of exhalation.

The ventilator, during inspiratory trigger decision operation 210,monitors patient and/or ventilator parameters or settings to determineif an inspiratory trigger threshold has been met and/or exceeded duringthe second portion of exhalation. The inspiratory trigger thresholdincludes any suitable condition or threshold for determining thatinspiration should be provided to the patient. During the second portionof exhalation, the inspiratory trigger threshold includes an inspiratorytrigger threshold substantially equal to or declining toward the desiredinspiratory trigger threshold as determined by second portion deliveryoperation 206.

If the ventilator during inspiratory trigger decision operation 210determines that the ventilator and/or patient parameters do not meet orexceed an inspiratory trigger threshold, the ventilator selects toperform second portion delivery operation 206. If the ventilator duringinspiratory trigger decision operation 210 determines that theventilator and/or patient parameters do meet or exceed an inspiratorytrigger threshold, the ventilator selects to perform inhale operation211. The performance of the inhale operation 211 ends the exhalationphase.

In additional embodiments, method 200 includes a display operation. Theventilator during the display operation displays any suitableinformation for display on a ventilator. In one embodiment, the displayoperation displays at least one of a minimum exhalation flow, a minimumexhalation time, a maximum exhalation time, a desired base flow, aninitial base flow, a desired inspiration trigger threshold, an initialinspiratory trigger threshold, an exhalation flow, an estimated leakflow, and an exhalation pressure.

Accordingly, in some embodiments, method 200 further includes acalculation operation. The ventilator during the calculation operationcalculates an exhaled tidal volume. The ventilator may utilize any knownmethods for calculating exhaled tidal volume. In some embodiments, theventilator during the calculation operation also calculates spirometry.In some embodiments, the spirometry calculation is based on thecalculated exhaled tidal volume. The ventilator may utilize any knownmethods for calculating spirometry.

In some embodiments, a microprocessor-based ventilator that accesses acomputer-readable medium having computer-executable instructions forperforming the method of ventilating a patient with a medical ventilatoris disclosed. This method includes repeatedly performing the stepsdisclosed in method 200 above and/or as illustrated in FIG. 2.

In some embodiments, the ventilator system includes: means fordetermining an initial base flow; means for determining an initialinspiratory trigger threshold; means for delivering the initial baseflow during at least a first portion of exhalation while setting theinspiratory trigger threshold to the initial inspiratory triggerthreshold; means for changing base flow from the initial base flowtoward a first flow value during at least a second portion ofexhalation; and means for decreasing the inspiratory trigger thresholdfrom the initial inspiratory trigger threshold toward a first triggerthreshold value while performing the step of changing the base flow.

As should be appreciated, the particular steps and methods describedherein are not exclusive and, as will be understood by those skilled inthe art, the particular ordering of steps as described herein is notintended to limit the method, e.g., steps may be performed in differingorder, additional steps may be performed, and disclosed steps may beexcluded without departing from the spirit of the present methods.

FIGS. 3A and 3B illustrate an embodiment of a method 300 for ventilatinga patient with a ventilator. As illustrated, method 300 begins at thestart of exhalation. As illustrated in FIG. 3A, method 300 includes aninitial base flow deliver operation 302, determine initial inspiratorytrigger threshold operation 303, decision operation 304 (illustrated as“Detect Initial Insp. Trigger”), decision operation 306 (illustrated as“Min. Exh. Time Expired?”), decision operation 308 (illustrated as “Max.Exh. Time Expired?”), and decision operation 312 (illustrated as “Exh.Flow less than Max. Exh. Flow?”), During the initial base flow deliveroperation 302, the ventilator delivers an initial base flow to thepatient during exhalation during at least a first portion of exhalation.During the initial base flow deliver operation 302, the ventilatorperforms determine initial inspiratory trigger threshold operation 303,decision operation 304, decision operation 306, decision operation 308,and decision operation 312.

The ventilator during the determine initial inspiratory triggerthreshold operation 303, determines an initial inspiratory triggerthreshold for the first portion of exhalation. In some embodiments,initial inspiratory trigger threshold is determined by the ventilator.In other embodiments, initial inspiratory trigger threshold isdetermined based on operator input or selection.

The ventilator during the decision operation 304 monitors patient and/orventilator parameters to determine if an inspiratory trigger thresholdhas been met and/or exceeded during the first portion of exhalation. Theinspiratory trigger threshold includes any suitable condition orthreshold for determining that inspiration should be provided to thepatient. During the first portion of exhalation, the inspiratorythreshold includes the initial inspiratory trigger threshold asdetermined by determine initial inspiratory trigger threshold operation303. For example, the initial inspiratory trigger threshold may requirea change of pressure of at least 6 to 10 cm of H₂O.

In some embodiments, method 300 detects changes in a ventilator and/orpatient parameter during the decision operation 304 via the monitoringof a respiratory gas pressure, the monitoring of lung flow, direct orindirect measurement of nerve impulses, or any other suitable method fordetecting changes in a ventilator parameter for comparison toinspiratory trigger thresholds. Method 300 may utilize sensors tomonitor the ventilator and/or patient parameters. Sensors may includeany suitable sensing device as known by a person of skill in the art fora ventilator. In some embodiments, the inspiratory trigger threshold maybe a change in exhalation pressure or a change in exhalation flow. Insome embodiments, the sensors are located in the pneumatic system, thebreathing circuit, and/or on the patient. In some embodiments, theventilator monitors the exhalation flow and/or exhalation pressure everycomputational cycle (e.g., 2 milliseconds, 5 milliseconds, 10milliseconds, etc.) during the deliver), of exhalation to determine ifthe inspiratory trigger threshold has been met and/or exceeded.

The ventilator during decision operation 304 compares the output of theone or more sensors to at least one inspiratory trigger threshold. Ifthe output meets and/or exceeds the one or more inspiratory triggerthresholds, the ventilator determines during decision operation 304 thatan inspiratory trigger is detected. If the output does not meet the oneor more inspiratory trigger thresholds, the ventilator determines duringdecision operation 304 that an inspiratory trigger is not detected. Ifthe ventilator determines that the inspiratory trigger is detectedduring the decision operation 304, the ventilator selects to performdeliver inspiratory operation 326 (illustrated as “Deliver Insp.Operation”). If the ventilator determines that the inspiratory triggeris not detected during the decision operation 304, the ventilatorselects to perform decision operation 306.

As illustrated in FIG. 3A, method 300 includes a deliver inspirationoperation 326. The ventilator during deliver inspiration operation 326delivers inspiration to the patient ending exhalation. The ventilatorperforms deliver inspiration operation 326 when a patient trigger isdetected. The ventilator delivers an inspiration based on ventilatorparameters, patient parameters, and/or input or selections from theoperator. For example, the inspiration provided by the ventilator may bebased on a selected breath type and/or mode of ventilation.

The ventilator during decision operation 306 determines if the minimumexhalation time has expired. As discussed above, the minimum exhalationtime refers to a predetermined amount of time in which it is unlikelythat a patient would desire to begin inspiration or would attempt totrigger an inspiration. If the ventilator determines that the minimumexhalation time has not expired during decision operation 306, theventilator selects to perform decision operation 304. If the ventilatordetermines that the minimum exhalation time has expired during decisionoperation 306, the ventilator selects to perform decision operation 308.In some embodiments, the ventilator determines if the minimum exhalationtime has expired by monitoring the output of sensors and/or bymonitoring calculations based on the output of sensors.

The ventilator during decision operation 308 determines if the maximumexhalation time has expired. As discussed above, the maximum exhalationtime refers to a predetermined amount of time after which it becomeshighly likely that a patient would attempt to trigger inspiration. Ifthe ventilator determines that the maximum exhalation time has notexpired during decision operation 308, the ventilator selects to performdecision operation 312. If the ventilator determines that the maximumexhalation time has expired during decision operation 308, theventilator selects to perform increasing base flow delivery operation310 (illustrated as “Incr. Base Flow Deliver Operation). In someembodiments, the ventilator determines if the maximum exhalation timehas expired by monitoring the output of sensors and/or by monitoringcalculations based on the output of sensors.

The ventilator during decision operation 312 determines if theexhalation flow is below the minimum exhalation flow. In someembodiments, the ventilator determines the exhalation flow by monitoringthe output of sensors and/or by monitoring calculations based on theoutput of sensors. The minimum exhalation flow refers to a predeterminedflow rate that when exhaled by the patient indicates that a patient isapproaching the end of active exhalation. In some embodiments, theminimum exhalation flow is zero. In some embodiments, the minimumexhalation flow is determined by the ventilator. In other embodiments,the minimum exhalation flow is set or determined by the operator viaoperator input or selection. If the ventilator determines that theexhalation flow is below the minimum exhalation flow during decisionoperation 312, the ventilator selects to perform increasing base flowdelivery operation 310. If the ventilator determines that the exhalationflow is not below the minimum exhalation flow during decision operation312, the ventilator selects to perform decision operation 304.

As further illustrated in FIG. 3A, method 300 includes an increasingbase flow delivery operation 310 (illustrated as “Incr. Base FlowDeliver Operation). The ventilator during the increasing base flowdelivery operation 310 increases the amount of base flow delivered tothe patient during exhalation at an exponential trajectory from theinitial base flow towards a desired base flow. The exponentialtrajectory is based on a constant. The constant is determined by theventilator. In some embodiments, the desired base flow is determined bythe ventilator. In other embodiments, the desired base flow is receivedby the ventilator via operator input or selection.

The increasing base flow delivery operation 310 is performed by theventilator during at least a second portion of exhalation. During theincreasing base flow delivery operation 310, the ventilator performsdecreasing inspiratory trigger threshold operation 314 (illustrated as“Deer. Insp. Trigger Operation”), decision operation 316 (illustrated as“Insp. Trigger Reach Desired Insp. Trigger?”), decision operation 318(illustrated as “Base Flow reach Desired Base Flow?”), and decisionoperation 324 (illustrated as “Detect Insp. Trigger?”) as illustrated inFIG. 3B.

As illustrated in FIG. 3B, method 300 includes a decreasing inspiratorytrigger threshold operation 314. The ventilator during the decreasinginspiratory trigger threshold operation 314 decreases the inspiratorytrigger threshold monitored by the ventilator during exhalation at anexponential trajectory from the initial inspiratory trigger thresholdtowards a desired inspiratory trigger threshold. The exponentialtrajectory is based on the same constant as utilized by the ventilatorduring the increasing base flow delivery operation 310 to determine thebase flow trajectory. In some embodiments, the desired inspiratorytrigger threshold is determined by the ventilator. In other embodiments,the desired inspiratory trigger threshold is received by the ventilatorvia operator input or selection. As discussed above the ventilatorperforms decreasing inspiratory trigger threshold operation 314 whileperforming the increasing base flow delivery operation 310. In someembodiments, the increasing base flow delivery operation 310 isperformed concurrently with the decreasing inspiratory trigger thresholdoperation 314 by the ventilator as illustrated in FIG. 4.

Method 300 includes a decision operation 316, decision operation 318,and decision operation 324. The order of the performance of the decisionoperation 316, the decision operation 318, and decision operation 324 isirrelevant. Accordingly, the decision operation 316, the decisionoperation 318, and decision operation 324 may be performed in any order,simultaneously, at different times, and/or at overlapping times.Further, the decision operation 316, the decision operation 318, anddecision operation 324 are all performed during at least the secondportion of exhalation.

The ventilator during decision operation 316 determines if theinspiratory trigger threshold has substantially reached the desiredinspiratory threshold. The ventilator may determine if the inspiratorytrigger threshold has substantially reached a desired inspiratorythreshold. If the ventilator determines that the inspiratory triggerthreshold has substantially reached the desired inspiratory thresholdduring decision operation 316, the ventilator selects to performmaintaining desired inspiratory trigger threshold operation 322(illustrated as “Maintain Desired Insp. Trigger Operation”). If theventilator determines that the inspiratory trigger threshold has notsubstantially reached the desired inspiratory threshold during decisionoperation 316, the ventilator selects to perform decision operation 318.

Further, method 300 includes a maintaining desired inspiratory triggerthreshold operation 322. The ventilator during the maintaining desiredinspiratory trigger threshold operation 322 sets and holds theinspiratory trigger threshold at the desired inspiratory triggerthreshold. The performance of the maintaining desired inspiratorytrigger threshold operation 322 ends the ventilator performance of thedecreasing inspiratory trigger threshold operation 314.

The ventilator during decision operation 318 determines if the deliveredbase flow has substantially reached the desired base flow. Theventilator may determine if the base flow has substantially reached thedesired base flow by monitoring the output of one or more sensors or bymonitoring calculations based on the output of one or more sensors. Ifthe ventilator determines that the base flow has substantially reachedthe desired base flow during decision operation 318, the ventilatorselects to perform desired base flow deliver operation 320. If theventilator determines that the base flow has not substantially reachedthe desired base flow during decision operation 318, the ventilatorselects to perform decision operation 324. As discussed above, thedesired inspiratory trigger threshold or the desired base flow issubstantially reached when the ventilator can no longer increase theamount of base flow provided without reaching or exceeding the desiredbase flow or when ventilator can no longer decrease the inspiratorytrigger threshold without reaching or exceeding the desired inspiratorytrigger threshold based on the sensitivity and precision of theventilator components.

As illustrated in FIG. 3B, method 300 includes a desired base flowdeliver operation 320. The ventilator during the desired base flowdeliver operation 320 sets and holds the base flow delivered to thepatient during at the second portion of exhalation at the desired baseflow. The performance of the desired base flow deliver operation 320ends the ventilator performance of the increasing base flow deliveryoperation 310.

Method 300 includes a decision operation 324. The ventilator during thedecision operation 324 monitors patient and/or ventilator parameters todetermine if an inspiratory trigger threshold has been met and/orexceeded during the second portion of exhalation. The inspiratorytrigger threshold includes any suitable condition or threshold fordetermining that inspiration should be provided to the patient. Duringthe second portion of exhalation, the inspiratory threshold includes thevarying inspiratory trigger threshold as determined by decreasinginspiratory trigger threshold operation 314.

In some embodiments, method 300 detects changes in a ventilator and/orpatient parameter during the decision operation 324 via the monitoringof a respiratory gas pressure, the monitoring of lung flow, direct orindirect measurement of nerve impulses, or any other suitable method fordetecting changes in a ventilator parameter for comparison toinspiratory trigger thresholds. Method 300 may utilize sensors tomonitor the ventilator and/or patient parameters. Sensors may includeany suitable sensing device as known by a person of skill in the art fora ventilator. In some embodiments, the inspiratory trigger threshold maybe a change in exhalation pressure or a change in exhalation flow. Insome embodiments, the sensors are located in the pneumatic system, thebreathing circuit, and/or on the patient. In some embodiments, theventilator monitors the exhalation flow and/or exhalation pressure everycomputational cycle (e.g., 2 milliseconds, 5 milliseconds, 10milliseconds, etc.) during the delivery of exhalation to determine ifthe inspiratory trigger threshold has been met and/or exceeded.

The ventilator during decision operation 324 compares the output of theone or more sensors to at least one inspiratory trigger threshold. Ifthe output meets and/or exceeds the one or more inspiratory triggerthreshold, the ventilator determines during decision operation 324 thatan inspiratory trigger is detected. If the output does not meet the oneor more inspiratory trigger thresholds, the ventilator determines duringdecision operation 324 that an inspiratory trigger is not detected. Ifthe ventilator determines that the inspiratory trigger is detectedduring the decision operation 324, the ventilator selects to performdeliver inspiration operation 326 (illustrated as “Deliver Insp.Operation”). If the ventilator determines that the inspiratory triggeris not detected during the decision operation 324, the ventilatorselects to perform increasing base flow delivery operation 310 asillustrated in FIG. 3A.

In some embodiments, method 300 includes an estimating operation and anadjusting operation. The ventilator during the estimating operationestimates the amount of flow leaked from a ventilation tubing systemduring ventilation. The ventilator may utilize any known methods forestimating the amount of flow leaked from the ventilation tubing system.The ventilator during the adjusting operation adds the estimated amountof leak flow to the initial base flow to account for the amount of flowleaked from the ventilation tubing system. Further, the ventilatorduring the adjusting operation may add the estimated amount of leak flowto a desired base flow to account for the amount of flow leaked from theventilation tubing system.

In other embodiments, method 300 includes a display operation. Theventilator during the display operation displays any suitableinformation for display on a ventilator. In one embodiment, the displayoperation displays at least one of a minimum exhalation flow, a minimumexhalation time, a maximum exhalation time, a desired base flow, adesired inspiratory trigger threshold, an inspiratory trigger threshold,a base flow, an exhalation flow, an estimated leak flow, and anexhalation pressure.

Method 300 decreases the inspiratory trigger threshold while the baseflow is being adjusted since the longer the exhalation period, the morelikely the patient will attempt to initiate an inspiratory trigger. Thedecrease in the inspiratory trigger threshold allows a patient to exertless effort to trigger a desired inspiration during the second portionof exhalation as it becomes more likely that a patient will attempt totrigger an inspiration.

Further, method 300 allows the ventilator to reduce the amount of baseflow delivered during exhalation. The smaller the ventilator-deliveredbase flow is during active exhalation, the smaller the uncertaintycontributed by measuring base flow by different sensors (once on thedelivery side and a second time as a portion of exhaust gas on theexhalation side). This is particularly advantageous under neonatalconditions when tidal volumes and exhaled flow rates are relativelysmaller and may be some orders of magnitude smaller than the base flow.Accordingly, method 300 allows the ventilator to more accuratelycalculate exhaled tidal volume and/or spirometry than ventilators thatutilize a constant base flow or a higher amount of base-flow duringactive exhalation.

Accordingly, in some embodiments, method 300 includes a calculationoperation. The ventilator during the calculation operation calculates anexhaled tidal volume. The ventilator may utilize any known methods forcalculating exhaled tidal volume. In some embodiments, the ventilatorduring the calculation operation also calculates spirometry. In someembodiments, the spirometry calculation is based on the calculatedexhaled tidal volume. The ventilator may utilize any known methods forcalculating spirometry.

In other embodiments, a microprocessor-based ventilator that accesses acomputer-readable medium having computer-executable instructions forperforming the method of ventilating a patient with a ventilator isdisclosed. This method includes repeatedly performing the stepsdisclosed in method 300 above and/or as illustrated in FIG. 3.

EXAMPLES Example 1

FIG. 4 illustrates an embodiment of a graph of delivered base flow andan inspiratory trigger threshold over time during an exhalation.According to this embodiment, a base flow change is executed at thebeginning of the exhalation phase. In this embodiment, the desiredinspiratory trigger threshold is 3 LPM and the desired base flow is 4.5LPM. In this embodiment, the first portion of exhalation ends upon theoccurrence of a condition, which starts the second portion ofexhalation. According to the illustrated embodiment, the conditionoccurs at 350 milliseconds (ms). The condition may include determiningthat a minimum exhalation time has expired, determining that anexhalation flow is below the minimum exhalation flow, determining thatthe exhalation flow is below the minimum exhalation flow prior toexpiration of a maximum exhalation time, and/or determining that themaximum exhalation time has expired.

In an embodiment as illustrated in FIG. 4, an initial inspiratorytrigger threshold of 10 LPM is set during the first portion ofexhalation. As illustrated in FIG. 4, an initial base flow of 1.5 LPM isdelivered during the first portion of exhalation. After the occurrenceof the condition and during the second portion of exhalation, asillustrated in FIG. 4, the inspiratory trigger threshold is decreasedexponentially while the delivered base flow is increased exponentiallyto reach 4.5 LPM. The inspiratory trigger threshold is decreased untilthe set inspiratory trigger threshold reaches the desired inspiratorytrigger threshold (3 LPM). Once the inspiratory trigger thresholdreaches the desired inspiratory trigger threshold, the inspiratorytrigger threshold is maintained at the desired inspiratory triggerthreshold. Further, the delivered base flow is increased until thedelivered base flow reaches the desired base flow. Once the deliveredbase flow reaches the desired base flow, the delivered base flow ismaintained at the desired base flow.

A patient initiated inspiration is not detected during the exhalationtime shown in FIG. 4. If an inspiratory trigger was detected,inspiration would be delivered upon detection ending the exhalationperiod.

Example 2

Example 2 illustrates an embodiment of a pseudo code for the systems andmethods of the disclosure. The pseudo code illustrated below utilizes analgorithm that incorporates the following aspects:

-   1) Base flow is initiated after the flow rate being exhaled by the    patient has reduced to a minimum threshold, which indicates that a    patient is approaching the end of active exhalation;-   2) Base flow will be delivered in accordance with an exponential    trajectory to reach a desired base flow within an optimum interval    to both maintain Positive End-Expiratory Pressure (PEEP) and to    minimize false triggering; and-   3) An inspiratory trigger threshold will be adaptively adjusted    (with an exponential trajectory) from a less sensitive threshold    (i.e., harder to trigger) at the start of exhalation phase and    decreasing smoothly to asymptote to a desired inspiratory trigger    threshold by the end of active exhalation or after allowing an    optimum interval concomitant with reaching the final base flow.    The pseudo code embodiment utilizing the algorithm described above    is listed below:-   //initialize-   filteredSensEx (inspiratory trigger threshold)=10.0 LPM-   //calculate a new base flow reference:-   leakAdd=estimated Value (estimated leak from the ventilator tubing    system);-   DesiredFlow=BaseFlow+leakAdd;-   MinQE (minimum exhalation flow)=1.5 LPM;-   MinTE (minimum exhalation time)=150 ms;-   Alpha (a constant)=0.05;-   MaxTE (maximum exhalation time)=500 ms;-   //every control cycle during exhalation phase execute the following.

IF (neonatal) {   IF (ExhTime < MinTE) {     DesiredFlow = leakAdd;    BaseFlowCheck = false;     filteredBaseFlow = 0; Sensitivity =setSensitivity+filteredSensEx; } Else {  IF (((Qexh < MinQE) AND(!BaseFlowCheck))   OR (exhTime > MaxTE))     BaseFlowCheck = true; }  IF (BaseFlowCheck)     {       filteredBaseFlow = filteredBaseFlow *      (1-alpha) + alpha * baseFlow;       DesiredFlow =filteredBaseFlow + leakAdd;       Sensitivity = setSensitivity +filteredSenEx * (1-alpha);       filteredSensEx = filteredSensEx *(1-alpha)     }   Else {       DesiredFlow = leakAdd;     } } // nochange if Adult or Pediatric settings.

Example 3

Example 3 illustrates an embodiment of a pseudo code for the systems andmethods of the disclosure. The pseudo code illustrated below utilizes analgorithm that incorporates the following aspects:

-   1) Base flow is initiated and regulated based on a current estimate    of the leak rate as exemplified above;-   2) An increase in leak rate is detected requiring adjustment of base    flow; and-   3) An inspiratory trigger threshold will be adaptively adjusted    (with an exponential trajectory) smoothly to asymptote to a desired    inspiratory trigger threshold by the end of transition period or    after allowing an optimum interval concomitant with reaching the    final base flow.

The pseudo code embodiment utilizing the algorithm described above islisted below upon detecting a change in leak rate:

-   //initialize-   filteredSensEx (inspiratory trigger threshold)=5.0 LPM-   //calculate new base flow and sensitivity references:-   OldLeakAdd=previous estimated Value (estimated leak from the    ventilator tubing system);-   NewLeakAdd=current estimated Value (updated estimated leak);-   filteredBaseFlow=BaseFlow+OldLeakAdd;-   DesiredBaseFlow=BaseFlow+NewLeakAdd;-   Sensitivity=setSensitivity+filteredSensEx;-   Alpha (a constant)=0.05;-   //Upon detecting a change in leak rate during exhalation and doing    the initialization above, perform the following every control cycle.

IF (Exhalation) {     filteredBaseFlow = filteredBaseFlow *    (1-alpha) + alpha * NewBaseFlow;     DesiredBaseFlow =filteredBaseFlow;     Sensitivity = setSensitivity + filteredSenEx *(1-alpha);     filteredSensEx = filteredSensEx * (1-alpha); }The pseudo code provided above is not meant to be limiting. Further,while values are provided in the embodiment of the pseudo code above,these values are not meant to be limiting and may vary based onventilator and/or patient parameters.

Those skilled in the art will recognize that the methods and systems ofthe present disclosure may be implemented in many manners and as suchare not to be limited by the foregoing exemplary embodiments andexamples. In other words, functional elements being performed by asingle or multiple components, in various combinations of hardware andsoftware or firmware, and individual functions, can be distributed amongsoftware applications at either the client or server level or both. Inthis regard, any number of the features of the different embodimentsdescribed herein may be combined into single or multiple embodiments,and alternate embodiments having fewer than or more than all of thefeatures herein described are possible. Functionality may also be, inwhole or in part, distributed among multiple components, in manners nowknown or to become known. Thus, myriad software/hardware/firmwarecombinations are possible in achieving the functions, features,interfaces and preferences described herein. Moreover, the scope of thepresent disclosure covers conventionally known manners for carrying outthe described features and functions and interfaces, and thosevariations and modifications that may be made to the hardware orsoftware firmware components described herein as would be understood bythose skilled in the art now and hereafter.

Numerous other changes may be made which will readily suggest themselvesto those skilled in the art and which are encompassed in the spirit ofthe disclosure and as defined in the appended claims. While variousembodiments have been described for purposes of this disclosure, variouschanges and modifications may be made which are well within the scope ofthe present invention. Numerous other changes may be made which willreadily suggest themselves to those skilled in the art and which areencompassed in the spirit of the disclosure and as defined in theclaims.

What is claimed is:
 1. A method for improving an accuracy of estimatingan exhalation volume while ventilating a patient with a ventilator, theventilator comprising at least one processor and at least one memory,the method comprising: delivering a base flow to a patient duringexhalation, wherein the base flow includes an estimated leak flow;determining, by the ventilator, an initial base flow; determining, bythe ventilator, an initial inspiratory trigger threshold; delivering theinitial base flow during at least a first portion of the exhalationwhile setting an inspiratory trigger threshold to the initialinspiratory trigger threshold; changing the base flow from the initialbase flow toward a subsequent base flow during at least a second portionof exhalation; decreasing the inspiratory trigger threshold from theinitial inspiratory trigger threshold toward a subsequent inspiratorytrigger threshold while changing the base flow; determining a change inthe estimated leak flow; progressively adjusting the base flow accordingto an exponential trajectory in a set time period during at least thesecond portion of exhalation to compensate for the determined change inthe estimated leak flow; and progressively adjusting the inspiratorytrigger threshold in the set time period.
 2. The method of claim 1,wherein a slope of the exponential trajectory of the base flow is basedon a time constant selected by the ventilator.
 3. The method of claim 1,wherein the step of decreasing the inspiratory trigger thresholdincludes decreasing the inspiratory trigger threshold according to anexponential trajectory.
 4. The method of claim 3, wherein a slope of theexponential trajectory of the inspiratory trigger threshold is based ona time constant selected by the ventilator.
 5. The method of claim 3,wherein a slope of the exponential trajectory of the base flow is basedon a first time constant and a slope of the exponential trajectory ofthe inspiratory trigger threshold is based on a second time constant. 6.The method of claim 5, wherein the first time constant and the secondtime constant are the same.
 7. The method of claim 1, wherein the settime period is less than or substantially equal to 200 ms.
 8. The methodof claim 1, wherein the determined change in the estimated leak flow isan increase in the estimated leak flow, and wherein the step ofprogressively adjusting the base flow includes increasing theinspiratory trigger threshold as a function of the determined increasein the estimated leak flow.
 9. The method of claim 1, wherein theinitial base flow is close to zero.
 10. The method of claim 1, whereinthe second portion of exhalation begins based on an occurrence of acondition.
 11. The method of claim 1, wherein adjusting the inspiratorytrigger threshold in the set time period is performed concurrently withthe progressively adjusting of the base flow in the set time period tocompensate for the determined change in the estimated leak flow.
 12. Themethod of claim 1, wherein the inspiratory trigger threshold is based onat least one of an exhalation flow and an exhalation pressure.
 13. Themethod of claim 1, further comprising: calculating an estimated exhaledtidal volume of the patient.
 14. The method of claim 1, furthercomprising: displaying at least one of: a minimum exhalation flow, aminimum exhalation time, a maximum exhalation time, the subsequent baseflow, the subsequent inspiratory trigger threshold, the inspiratorytrigger threshold, the base flow, an exhalation flow, the estimated leakflow, the determined change in the estimated leak flow, the set periodof time, and an exhalation pressure.
 15. A ventilator system comprising:a pressure generating system configured to generate a flow of breathinggas; a ventilation tubing system including a patient interfaceconfigured to connect the pressure generating system to a patient; atleast one sensor operatively coupled to at least one of the pressuregenerating system and the ventilation tubing system; a leak estimationmodule configured to determine a change in an estimated leak flow in theventilation tubing system by utilizing output from the at least onesensor; a base flow trajectory module configured to deliver a base flowincluding the estimated leak flow during exhalation to the patient,wherein the base flow trajectory module changes the base flow deliveredto the patient from an initial base flow toward a subsequent base flowduring at least a portion of the exhalation, and wherein the base flowtrajectory module progressively adjusts the base flow according to anexponential trajectory during a set time period during the exhalation tocompensate for the determined change in the estimated leak flow; aninspiratory trigger threshold trajectory module configured to set aninspiratory trigger threshold during exhalation, wherein the inspiratorytrigger threshold trajectory module decreases the inspiratory triggerthreshold from an initial inspiratory trigger threshold towards asubsequent inspiratory trigger threshold while the base flow trajectorymodule changes the base flow delivered to the patient; and a processorin communication with the pressure generating system, the at least onesensor, the leak estimation module, the inspiratory trigger thresholdtrajectory module, and the base flow trajectory module.
 16. Theventilator system of claim 15, further comprising: a display incommunication with processor, the display configured to display at leastone of a minimum exhalation flow, a minimum exhalation time, a maximumexhalation time, the subsequent base flow, the subsequent inspiratorytrigger threshold, the inspiratory trigger threshold, the base flow, anexhalation flow, the estimated leak flow, and an exhalation pressure.17. The ventilator system of claim 15, wherein the processor isconfigured to calculate an estimated exhaled tidal volume based on theoutput from the at least one sensor.
 18. The method of claim 15, whereina slope of the exponential trajectory is based on a time constant.